The thermodynamic method used in nearly all air conditioners, refrigerators and heat pumps is the vapor compression cycle also called the refrigeration cycle. The cycle uses four primary components: a compressor, a condenser, an expansion device, and an evaporator; some systems may use additional components such as a receiver, additional heat exchangers, two or more compressors, and/or an accumulator and other specialized components. The four primary components are piped in series to form a closed loop system that carries out the changes in temperature, pressure and state of the working fluid refrigerant that form the vapor compression cycle. Furthermore, within air conditioners, refrigerators, and heat pumps outside of the refrigeration cycle there are typically ancillary components that move the desired heat transfer medium, such as the blowing of air or of flowing of water that is to be cooled or heated, across the primary heat exchangers being the condenser coil and the evaporator coil. In addition there is typically a control circuit that energizes and de-energizes the driven components including the compressor and such as fan motors, pump motors, damper actuators, and valves accordingly to meet a desired temperature, ventilation and/or humidity or other set points and operating parameters.
The efficiency of vapor compression cycles is conventionally given by an energy efficiency ratio (EER) and/or a coefficient of performance (COP). The EER generally refers to the air conditioning, refrigerating or heating system and is the ratio of the heat absorbed by the evaporator cooling coil over the input power to the equipment, or conversely for heat pumps, the rate of heat rejected by the condenser heating coil over the input power to the equipment. EER is defined as the ratio of cooling or heating provided to electric power consumed, in units of kBTU/hr per kW. EER varies greatly with cooling load, refrigerant level and airflow, among other factors. The COP generally refers to the thermodynamic cycle and is defined as the ratio of the heat absorption rate from the evaporator over the rate of input work provided to the cycle, or conversely for heat pumps, the rate of heat rejection by the condenser over the rate of input work provided to the cycle. COP is a unitless numerical ratio. In addition, there is a standard weighted average of EER at various conditions known as the integrated energy efficiency ratio (IEER).
The efficiency of an air conditioner or heat pump system is needed to accurately calculate the electrical costs of operating the system to provide a known amount of cooling. Significant degradation of the air-conditioner, refrigerator, or heat pump components over time, such as refrigerant loss, compressor wear, or fouled heat exchangers, increase the operating cost by lowering the capacity of the system and/or increasing the power consumption. Either effect of lowering capacity or increasing power manifest in reduced energy efficiency and a reduced EER, COP and IEER while correcting or mitigating degradations will restore efficiency and manifest in an increased EER.
The measured EER and COP are affected by the load under which the air conditioning, refrigeration or heating system is running; the load is a function of the evaporating and condensing temperatures. An increase in evaporating temperature will raise the measured EER and COP, as will a decrease in condensing temperature; as can be predicted by the thermodynamic cycle parameters. Likewise, lower evaporating temperature will reduce the measured EER and COP, as will higher condensing temperature.
Having the actual operating EER is key to improving efficiency, because it provides an absolute, realistic assessment of current condition with feedback so operating parameters can be adjusted and maintenance needs can be identified. Measuring the EER, COP and JEER of systems based on the vapor compression cycle is difficult, more so while operating in a field environment rather than a test laboratory. An accurate heat absorption measurement for these systems is quite complex and requires measurement of the mass flow rate of fluid through the heat exchanger along with enthalpies entering and leaving the heat exchanger. The prior art uses estimating methods, circuitous logic trees, or manufacturer's published data as a substitute for actual mass flow rate measurement, and temperatures as a substitute for enthalpy determination. A simultaneous power measurement along with the heat absorption measurement is required for an accurate EER calculation result; prior art uses manufacturer's published tables or polynomial equations as a substitute for actual power measurement. The use of manufacturer's published capacity or power data inherently assumes the compressor is in like-new condition, as in the manufacturer's laboratory when an un-used sample was tested under ideal conditions to produce the published data. Consequently, the effects of degradation, such as a worn compressor or a change in oil properties, under typical field conditions on the primary system components and the actual operating EER and COP is largely missed by the prior art.
The prior art methods and devices do not result in an EER or an IEER measurement that is directly comparable against measurements made at different loads, evaporating or condensing temperatures of the same system over time, nor against other systems, nor against published standard efficiency ratings; rather the prior art measurements are relativistic not absolute values and thus application is mostly limited to before versus after comparisons of a certain system operating under the load conditions at a particular time. An efficiency meter by Schulz, Sr. (U.S. Pat. No. 4,186,563) does not actually measure efficiency in absolute units, rather, it provides a relative measurement that cannot be compared against other units or performance specifications. A coefficient of performance measuring device by Brantly, et al. (U.S. Pat. No. 4,432,232) gives an indirect indication of efficiency based on air measurements that include only sensible cooling and neglect dehumidification latent cooling, and relies on inaccurate airflow and single point air temperature measurements. Another coefficient of performance measuring device by MacArthur, et al. (U.S. Pat. No. 4,510,576) relies on stored motor loss tables and compressor manufacturer data, and thus cannot take into account the degradation in compressor performance over time versus the performance of a new, laboratory tested compressor. An invention by Rossi, et al. (U.S. Pat. No. 6,701,725) does not make an actual measurement of energy efficiency, rather, it relies upon manufacturer's compressor performance data to make an indirect estimate of energy efficiency, and thus does not take into account real versus rated compressor performance degradation. A method by Mowris (U.S. Pat. No. 8,583,384) makes only a relative estimate of the improvement in energy efficiency and does not provide an absolute measurement of energy efficiency, rather, it relies on temperature differences relative to standard tables to infer a diagnosis. An application by Bersch et al. (US 20100153057 A1) describing a method for determining the coefficient of performance, which relies on an indirect calculation of power usage by the compressor, rather than an accurate power measurement, and neglects motor, frictional, volumetric and other compressor losses and does not make a refrigerating capacity measurement.